Maltese Medical Journal, 1997; 9 (1): 28
All rights reserved
Age and sex distribution of adult asthma admission A study of the five-year cumulative prevalence M.V. 8alzan*
l
!
ABSTRACT: Objective - to describe the age and sex distribution of adult patients (ages 15-59) in
Malta, admitted because of severe acute asthma.
Design - retrospective review of all acute adult asthma admissions to determine the 5-year
cumulative prevalence of acute asthma admission.
Setting - all adult medical admissions from 1989 to 1993 to St. Luke's Hospital, the only acute
medical facility serving the whole of the island of Malta.
Results - in 1993, 304 patients in the 20-59 age group were admitted at least once in five years. The
distribution of the age specific five year cumulative prevalence of asthma admission is a U shaped
curve (p<O.OOI). The first peak is in the 20-24 age group 245.8 per 100,000 (95% CI:309.2-182.3)
and the second peak is in the 55-59 age group 246.7 per 100,000 (95% CI:322.1-171.3). A trough is
present in the 35-39 age group, 100.1 per 100,000 (95% CI:137.9-62.3). Of the whole 20-59 age
group, 61.8% are female (p<O.OI). This female predominance is most evident in the 30-39 and 40­
49 age groups, 64.1 % (p<0.05) and 73.2% (p<O.OI) respectively. In the 20-59 age group, 69% of
male patients were admitted only once in five years, 29.3% 2-5 times and 1.7% more than five
times as compared to 66%, 29.8% and 4.2% respectively in females.
Conclusion - The female predominance in adult asthma admission rates reflects a larger number of
female patients who require hospital admission rather than higher admission rates per person in
females as compared to males.
* Department of Medicine, St. Luke's Hospital, Gwardamangia
Correspondence:
M.V. Balzan, Department of Medicine, SI. Luke's Hospital, Gwardamangia
Keywords:
asthma admission, cumulative prevalence, gender distribution
Introduction
Although acute severe asthma is one of the most
common causes for hospital admission in young and
middle aged adults, only a few papers have been
published on the age and sex distribution of asthma
hospital admission. The greatest difficulty with such
epidemiological studies is determining the exact
denominator population from which such admissions
arise. Two papers have looked at the asthma admission
rate in the whole Finnish I and Danish 2 populations
respectively.
A system of computerized personal
identification numbers in these countries made these
studies feasible.
Both these studies suggest that adult asthma admission
rates are higher in females. A similar gender distribution
was also noted in the United States 3.4. However, in a
stud y in Lom bard y, Ital y5, there appeared to be no
difference between male and female admission rates for
adults.
The above studies measured admissions rather than
individual patients. Skobeloff et al 6 in south eastern
Pennsylvania opted to count every patient once every
year and obtained similar results. The aim of the study
presented here was to establish whether the higher
female admission rate is due to a larger number of
female patients requiring admission or due to a higher
admission rate per patient in females as compared to
males. For this reason every patient was counted only
once every five years. To be included in the study at the
end of 1993, a patient would have to have been admitted
to hospital with asthma at least once in the preceding
five years.
Patients and methods - the study population
The study was conducted on the island of Malta.
Every individual residing permanently on the island has
a personal identification number, so accurate population
The
data for the years 1989-93 was available 7 .
popUlation of the sister island, Gozo, was excluded from
the study.
Acute asthma hospital admissions
All acute asthma patients presenting to hospital are
seen by casualty medical officers.
However, all
admissions are reviewed by registrars or senior registrars
before entry. Casualty officers personally enter the
diagnosis and the main reason for admission on a special
register. The admission diagnosis of asthma was based
on the guidelines of the International Classification of
Diseases, Ninth Revision (ICD 9)8 code 493.0.
A team of four doctors manually reviewed the registers
covering all acute medical admissions from January 1st
1989 to 31st December 1993. All admissions where
acute asthma was the principal reason for admission
were recorded. Cases where asthma was not the main
--, Age and sex distribution of adult asthma admission
reason for admission, or where it was not clear whether
the problem was bronchitis or acute asthma, were not
included. The age, gender, identification number and
date of admission were recorded for all cases.
Data for children under 14 years of age on the day of
admission were not available as these children are seen
in a separate paediatric department. Patients over 59
years of age in the year of admission were excluded
because of the decreased reliability of the diagnosis of
asthma. All foreign patients residing temporarily on the
island, i.e. no personal identification number, were
excluded. These data were entered into a computer
database (dbaseIV 1.5) for analysis.
Age'"
( 11)
2()· 24 57
25-29 ]2
:10-:14 3<)
27
Pre"\ a h.:n !..d9 ~ f)o(, "1)>;0:*
PoruJ~lIiOI1·
2.~.19 1 14~ ~ 1.~09 . : -IS : .. ) 22.1 .. 1 143,9 (1'I.~5 -94 3) 26.572 146.8 (192 .8 -IOO . ~ ) 26.960 100.l 26,767 175,6 40-44 47
4 5-49 .35
2 K..~()()
5()-S4
26
15.82.1 164.3
5 5-5 ~
41
16.6 1X l~6 .7 (.122 ]
1l3.7 r abl. 1. Age ltl,(rlbution ur ~ ' oar Cll lll ll la!l\e pt e"alell er li t' ,\slhm. ho'pilallldm;,. ion 1989-93. (0= 304) s · 2038. Jf - .1" 0 OIl 1 - ,': 11 .. ,
l)ect'mh~r
- ' ~r )()U.OOO
lUln
!X'pulauon
Five-year cumulative prevalence
Any patient admitted during the study period was
counted only once irrespective of the number of
admissions. The age was calculated by subtracting the
birth year from 1993. The popUlation on 31st December
1993 7 was used as denominator for age and gender
stratification. In determining the cumulative prevalence
of the 20-29 age group, admissions which had occurred
from 1989 to 1992 when the patient would have been
under 20 years of age, were taken into consideration.
For each patient the number of admissions from 1989 to
1993 was determined.
29
oldest age groups. (x 2
p<O.OOI).
= 26.38, at 7 degrees
of freedom
Admissions per capita
The number of admissions for every patient was
calculated. Patients were divided into three groups,
representing one admission, two to five admissions and
more than five admissions in five years. Although
separation into smaller groups is, in theory, preferable,
the numbers would have been too small for proper
statistical analysis when comparing males with females.
Although the number of patients with more than five
admissions was very small, they accounted for a large
proportion of the admissions.
It was decided to
eliminate these patients from the analysis of patients
with multiple admissions to avoid serious bias to the
otherwise large group of patients with multiple
admissions.
Statistics
A goodness of fit x2 test was performed comparing the
measured crude cumulative 5-year prevalence in each
five year age group with random distribution. A simple
paired Hest was used to compare the measured gender
distribution with the expected sex distribution as based
on the demographic data. A Hest was also used to
compare the male and female rates for the distribution of
patients by number of admissions.
Results
From 1st January 1989 to 31st December 1993 there
were 696 admissions for severe acute asthma to St.
Luke's Hospital in the 15-59 age group. The age specific
5-year cumulative prevalence rates for asthma admission
in 5-year age groups from 20 to 59 years of age are
shown in Table 1 and Figure 1. A U shaped curve is
observed with the highest rates in the youngest and
Figure 2 shows the gender distribution by age group of
the cumulative 5-year prevalence of acute asthma
admissions. In Table 2, the observed sex distribution of
the 5-year cumulative prevalence of acute asthma
admission is compared with predicted values based on
demographic data. When the whole 20-59 age group is
taken into consideration, there is a statistically
significant female predominance in the cumulative
prevalence. This is more evident in the 30-39 and 40-49
age groups. Although a female predominance is also
present in the 20-29 age group, this fails to reach
statistical significance probably because the numbers are
too small. In the 50-59 age group, there is no significant
difference between males and females.
In Figure 3, data is presented in three groups, each
group representing the number of admissions per patient
in five years.
There is no statistically significant
difference between male and female rates. However,
M.V. Balzan
30
Age
Predic ted va ju (~s
l, ~ij :e
Fe ' ;,of.'/-" -'
Population'
,'/ r" ,'."'
::'>( 1
30-39
40 ··49
/ i. ':.': ~)6
50·59
16
0::;9
':'e8 ;::;'47 9
20-59
45 .8
33.9
41 ,1
22,C~)1
20·29
8~>
60
.,,";;
~C(\
34 (C.O ·
:'. 2 0
:-: I.i,U 9>' , ~: 1:::
30~ 116, R ..:~ ..-, 188 ' 0 1 fI '~
1!. 3 ?
•
" Ci 35.0
(">
.1
41 43.2 i -if' ,;, :
32 , 1 ":1'
~ ')01 , 40 .9
r, ..· rl )
:)- J () ~
0' ;:)0'
'.; . )
!'l .' -" ., 1 5'O~8 ~-
Tablc 2. Gender dlsinbut lO'\ b, .•gf- nroup of th e UJd~ ~. ': t>a , ~, UPl u ' at nj e
pre,.' Cllp·,c ',: :'If !\sthr~la adn llSSIOr. i le/89 -93)
"N ::> no! ";lynlll(~I)!
I
I ·~· ,­
D2S
0 1
80'\,
W-.
40>"
;<J'.
0".,
Fernale
Ma ie
Figure 3, Five year cumulative prevalence of asthma admission 15·59
Distribution according to the number 01 admiSSions in 5 years
Figure 4 shows that there is a gradual increase in the
number of admissions per capita with increasing age in
both males and females in those patients admitted
between two and five times in five years. However,
once again, there is no significant difference between
sexes in the admission rates per person in each age
group.
[DF~UM""I
!
;;~;
~
~
~
study 2. However. the data from the Maltese
study would suggest that the higher admission
'."a ':,1":
rate in the older age group is more likely to be
due to the larger number of patients requiring
acute asthma admission rather than more
frequent admissions per patient. Although
OC;·;-~there appears to be a higher admission rate per
capita in the older age groups. this is too small
to account for the higher prevalence in the
older age groups by itself.
The distribution of admissions per patient is
the same in both sexes. This suggests that the higher
admission rate in females is due to a larger number of
different patients requiring admission rather than a higher
admission rate per capita in females as compared to
males. In the 50-59 age group, males appear to catch up
with females both in the 5-year cumulative prevalence
and admission rate. This was observed in the Danish 2 but
not in the South Pennsylvania 6 study.
The gender distribution in Malta follows a very similar
pattern to that of the 5-year cumulative prevalence of
patients suffering from asthma and not requiring
admissions in the Tucson community9.1O. Again, in this
study males appeared to catch up with females in the 50­
59 age group . A comparable age and sex distribution for
the prevalence of asthma in the general population was
also described in Minnesota 11 .
lt is not known why severe asthma is commoner in
females, however hormonal differences of asthma in
pregnancy have been proposed 6 . However, it is possible
that males catch up with females in the older age group.
because smoking related illness is commoner in the older
age groups. Although no data on smoking were available
in this study. it is possible that a number of patients with
smoking related wheezy bronchitis could have been
wrongly diagnosed as asthma. However. in the Tucson
study9,1O. where patients were thoroughly evaluated,
prospectively. the same pattern of increased male asthma
prevalence in the older age groups was present even
when smoking was excluded. This would suggest that
there are other, yet undetermined factors accounting for
the rise in prevalence in males in the older age groups .
15
,,~ s
[
01.
Conclusion
G ~;
:i029
40·49
Age group
Figure 4. Ad missi ons per patient in five years
in patients with 2-5 admi&&ioo6
Discussion
In this paper, data on asthma admission from 1989 to
1993 is presented as the 5-year cumulative prevalence.
Using this method, patients rather than admissions are
counted. The two Scandinavian papers 1.2 have looked
only at the admission rates without determining the
yearly prevalence, i.e. the number of patients per year.
Furthermore, in the Maltese study. every patient is
counted only once in five years, rather than once every
year of admission as in the South Pennsylvania study6.
The distribution of patients by age is U shaped. A
progressive decrease in childhood onset asthma
followed by a progressive increase in the prevalence of
adult onset asthma would explain the two limbs of the
U-shaped curve. This confirms the results of the Danish
The 5-year cumulative prevalence of acute asthma
admission for adults aged 20-59 in the island of Malta
has been determined from 1989 to 1993. Although this
study has a different epidemiological approach to three
other important studies in determining the age and sex
distribution of acute asthma admission, the results are
very similar.
A U shaped distribution of the age specific 5-year
cumulative prevalence is present. The higher female
admission rates are the result of a higher prevalence of
female asthma patients requiring admission rather than to
more severe asthma with more frequent exacerbations per
patient in females as compared to males.
Acknowledgements
The author would like to thank Dr. Edward Melillo. Dr.
Joanna Camilleri and Dr. John Cauchi for helping me
review the admission registers.
Age and sex distribution of adult asthma admission
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